The use of carbon dioxide spray systems for cleaning data storage disks is described in, for example, U.S. Pat. No. 5,419,733 (Johnson et al.). As discussed there, cleaning of data storage disks during manufacturing is particularly useful when tracks and other features are written into the surface of the disk using, e.g., laser energy. Such techniques can generate debris that can adversely affect the product if not removed before, during, and after processing. They may also affect the equipment in which the disks are to be used.
One potential problem with using conventional carbon dioxide cleaning systems is that the temperature of the disk surface will be lowered by the frozen carbon dioxide particles used for cleaning. If the disk surface temperature falls below the dew point of the air in which the disk is located, moisture can condense on the disk surface and, in some instances, frost can form on the disk surface. Both of those conditions, i.e., liquid or frozen water on the disk surface, severely impact the efficacy of the cleaning processes.
To reduce the likelihood of condensation on the disk surface, a variety of techniques have been employed. One solution is to increase the cycle time of the manufacturing equipment to allow the surface temperature of the disk to rise. That additional cycle time, however, impacts overall productivity and is not favored.
Another approach is to lower the dew point of the cleaning environment. This could be accomplished by drying the air in which the disk is located or purging the environment with a dry inert gas (e.g., nitrogen). This approach does, however, add additional cost to the cleaning process. Also, maintaining a closed or semisealed environment is not very conducive to high volume production in which many parts are continuously entering and exiting the cleaning system.
U.S. Pat. No. 5,419,733 (Johnson et al.) discloses a system involving a heated chuck on which the disk is located (where the term "chuck" as used by Johnson et al. includes both the spindle and the platform surrounding the spindle). The heat from the chuck is then transferred to those portions of the data storage medium in contact with the chuck through conduction. Likewise, the hub is also typically heated because at least a portion of the hub is in direct contact with the chuck during operation of the cleaning system.
One problem associated with the cleaning process and system discussed by Johnson et al. is that no provision is made for the thickness of the outer flange of the hub on the data storage disk. As a result, the portion of the data storage media near the hub is typically spaced from or lifted off of the chuck. That space limits the effectiveness of the heat transfer from the chuck to the portion of the media directly surrounding the hub. With the reduced heat transfer to counter the cooling effect of the carbon dioxide crystals, the surface temperature of the media is more likely to fall below the ambient dew point. Once the media surface temperature falls below the ambient dew point, condensation can form on the media surface and reduce the effectiveness of the carbon dioxide cleaning process.
Also, because the hub is heated and the data storage media directly surrounding the hub is rapidly cooled during the cleaning process, a temperature gradient can be induced across the boundary between the hub and the media surrounding the hub. That temperature gradient exists in spite of the heating of the media further away from the hub and in contact with the chuck because the rate of heat transfer through the data storage media itself is relatively low. As a result, the adhesives or other bonding agents used to attach the data storage media to the hub can become embrittled due to freezing and may, in some instances, crack. The cracks can reduce the strength of the bond between the data storage media and the hub.
As a result, a need exists for a simple and effective solution for preventing condensation on the surface of a data storage disk in a carbon dioxide cleaning system while preserving the integrity of the hub to media bond.